Let’s say that there are wooden tablets that touch one another at their corners and that are raised from the ground by the space of a handbreadth. If there’s ritual impurity under one of them, then one who touches the next tablet is rendered unclean with seven-day impurity. Utensils under the first tablet are rendered ritually unclean but those under the next tablet remain clean. A table doesn’t convey ritual impurity unless it includes a square with the space of a handbreadth.
If jars were standing on their bases or lying on their sides in the open air, touching one another in the space of a handbreadth, then if there’s ritual impurity under one of them, the uncleanliness extends upwards and downwards. This is the case when the jars are ritually clean; if they’re ritually unclean or raised the space of a handbreadth from the ground, then if there’s ritual impurity under one of them, what’s under all of them is rendered unclean.